The present invention relates to a disc drive microactuator, and more particularly to a method of singulation of microactuator devices from a silicon wafer.
The density of concentric data tracks on magnetic discs continues to increase (that is, the size of data tracks and radial spacing between data tracks continues to decrease), requiring more precise radial positioning of the head. Conventionally, head-positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a head on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks.
One promising approach for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby effecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. One design involves inserting a silicon-based thin film structure between the suspension and the slider in a disc drive assembly. Such a design must be realized in a relatively small wafer area, to keep costs reasonable and to allow easy integration into the disc drive design.
After fabrication of the structure is completed, the final process step for nearly all microelectromechanical systems (MEMS), including the microactuator design discussed herein, is singulation of the devices from the wafer. Due to the cost efficiency of wafer processing versus individual device processing, it is desirable to keep the devices in wafer form for as many process steps as possible.
Dicing with saw blades is the most common method of singulation, but requires that the device features be protected from the water and debris generated by the sawing. Device singulation can be done by the final structure etch for devices that are etched through the wafer. Small tabs of silicon can be left unetched to hold the devices in place for fabrication of features of the device, but it is very difficult to control the dimensions of the tab so that it will reliably hold the devices in place, yet break off easily when desired without damaging the device. This is because the tabs for devices that are 200 micrometers (xcexcm) thick would have to be approximately 1 xcexcm wide to break reliably under a vertical load, as would be applied by automated equipment. Tabs this narrow cannot be produced in a controllable manner, and would be susceptible to accidental breakage from unintentional forces applied in the plane of the wafer.
The present invention is a method for singulation of MEMS devices from a substrate wafer. Singulation is performed by first masking the substrate wafer to define a channel around a periphery of each of the MEMS devices on the substrate wafer. The channel has a first width along a first portion of the channel and a second width less than the first width along a second portion of the channel. The substrate wafer is then etched using a reactive ion etching (RIE) process, thus separating the MEMS devices from the substrate wafer along the first portion of the channel and forming breakable tethers that connect the MEMS devices to the substrate wafer along the second portion of the channel.